Is wearing underwear made of silk forbidden, even if it is for oneself and not for show-off?

It is forbidden for men to wear clothes made of natural silk, due to what has been established that the Prophet, may Allah's prayers and peace be upon him, said regarding gold and silk: "These two are forbidden for the males of my Ummah." As for artificial silk, it is not forbidden, but it is preferable to avoid it if it strongly resembles natural silk.